Although there is an important genetic contribution to the normal range of variation seen in human behaviors as well as human behavioral disorders, very little is known about the genes that influence behavior in any organism. In particular, there are currently few model vertebrate systems in which the study of behavioral variation in a natural, outbred population can be genetically dissected. The recent development of genetic and genomic tools for the threespine stickleback (Gasterosteus aculeatus) presents an opportunity to study the genetic basis of behavioral variation in a well-defined ecological and evolutionary context. The mating behaviors of the threespine stickleback are perhaps the best-studied of any animal system. Previous work has shown that divergence in male and female mating behaviors leads to reproductive isolation between stickleback populations that have adapted to living in two different habitats ('benthic' and 'limnetic') in a single lake. There are multiple lakes in British Columbia in which these benthic and limnetic 'species pairs' have evolved, and similar changes in mating behavior have occurred independently in each lake. The aim of this study is to investigate the genetic underpinnings of behaviors involved in reproductive isolation between benthic and limnetic sticklebacks from two lakes (Priest and Paxton) using quantitative trait locus (QTL) mapping. These experimental populations will be raised and behaviorally evaluated under fully natural conditions in outdoor ponds. By investigating the genetic basis of behavioral phenotypes involved in reproductive isolation (e.g., male nesting behavior and female mate preferences), this work will test whether parallel species pairs of sticklebacks in isolated lakes share similar genetic architectures for convergent behaviors involved in reproductive isolation. This project will also test whether QTL influencing behaviors involved in reproductive isolation map disproportionately to genomic regions affecting traits known to be important for mate selection, such as body size and shape. Importantly, the QTL mapping experiments proposed here will serve as a first step in the identification of genes that underlie behavioral differences in natural stickleback populations. Results in sticklebacks are likely to have important implications for understanding the genetic basis of behavioral variation and behavioral disorders in humans because many of the genetic and neural pathways that underlie behaviors are likely to be conserved between fish and humans. In addition, humans and sticklebacks have migrated and adapted to new environments over a similar evolutionary timeframe, suggesting that studying the genetic architecture of behavioral variation in sticklebacks has direct relevance to similar studies in humans. [unreadable] [unreadable] [unreadable] [unreadable]